My Guess is, the officer at poe routinely question people on why they are here.
Since your friend had got visa 2 years ago, officer would have questioned on why he is coming now ? does he really have a client to work for?
your friend might have got panicked and said some inconsisting answers.
INS knows that some people have visa with one company and join another one without even working for the 1st one. (ins thinks it is fraud.)
That was the reason they enquired about your friend to his employer.
As by your words, the employer replied in negative about your friends arrival.
It is your friends fault for not informing the employer. (may be he decided to work for someone else)
In my opinion, the Employer may not be a fraud.
The Reason why Lufthansa called you is, may be your friend had given your number for contact. (as he cannot make any calls)
I will tell you a incident happened in 95 at singapore.
One of my friend went for H1B visa at usa consulate.
The officer asked whether he had got a client.
My friend told that he have a client and gave the address & phone no. (his employer had asked him to say).
The officer immediately contacted the client to verify it.
On getting the negative reply from the client, he told my friend not to step into the embassy for the same visa again for 2 years as he would automatically reject it.
My friend never stepped in us consulate at singapore again.
Meow